(1) Field of the Invention
The present invention relates to a three-way valve, and more particularly to a three-way valve that includes the three ports of a high-pressure port, a medium-pressure port, and a low-pressure port, and performs switching between a flow path causing the fluid to flow from the high-pressure port to the medium-pressure port and a flow path causing the fluid to flow from the medium-pressure port to the low-pressure port.
(2) Description of the Related Art
The three-way valve includes a type that utilizes the pressure of fluid introduced therein, for switching operation of a main valve thereof. The three-way valve of this type includes a valve element for selectively opening and closing a passage between a first port and a second port of three ports, and a passage between the second port and a third port of the same, and pistons for driving the valve element in valve-opening and valve-closing directions, respectively, such that the pressure of upstream-side fluid is introduced into a pressure chamber of one of the pistons, while the pressure of a pressure chamber of the other of the pistons is released, to thereby cause the pistons to actuate the valve element for opening and closing operations. To switch the pressure chamber of each piston between a state connected to the high-pressure side and a state connected to the low-pressure side, a solenoid-operated pilot valve is used. This pilot valve has a three-way valve structure and introduces or releases pressure into or from the pressure chamber of the associated piston by energization or deenergization of a solenoid thereof. For the pilot valves provided in the three-way valve, pressure passages for connecting between the upstream side of the three-way valve, the pressure chambers of the pistons, and the low-pressure side of the three-way valve are formed by capillary tubes or the like (Japanese Laid-Open Utility Model Publication (Kokai) No. H05-64582 (drain passages 29 and 30 in FIG. 1)).
In the conventional three-way valve, however, it is necessary to form the pressure passages for switching the pressure in each of the pressure chambers of the pistons e.g. by capillary tubes, and further each pilot valve has a three-way valve structure. This increases the number of component parts and man-hours for assembling the component parts.